1. Field of the Invention
The invention relates to a system for recording and displaying a series of images on a record carrier, which system includes an image encoding and recording unit for recording images in at least a first and a second data stream, and an image information retrieval unit for displaying images stored on the record carrier, which image information retrieval unit has a first and a second mode of operation, in the first mode of operation images originating from the first data stream being displayed whereas in the second mode of operation images from the second data stream are displayed. The invention also relates to an image encoding and recording unit and an image information retrieval unit for use in such a system.
2. Description of the Related Art
A system of this kind is described in the previous European Patent Application No. 94202922.4 (which corresponds to U.S. patent application Ser. No. 08/294,129, filed Aug. 22, 1994 and can be used, for example in medical diagnostic applications for storing X-ray images in digital form. The diagnostic X-ray images can be displayed in various ways, for example with a high and with a low resolution, as stationary images or as moving images. As is described in the cited previous Application, the requirements imposed on the various display methods, in conjunction with the technical limitations of the recording and retrieval units, are optimally satisfied by recording the images on the record carrier in different data streams and by using a different data stream for display in conformity with the desired display method.
In practice the recorded "raw" X-ray images are subjected to various image processing operations before they are displayed. An important reason for image processing is the elimination or reduction of image artefacts introduced by the recording equipment, for example distortions or vignetting introduced by the optical system and elements which are visible in the image, for example the scatter radiation grid or the lead shutters of the collimator. Other reasons are the elimination of overexposed or uninteresting but disturbing parts of the image from the image displayed, the adaptation of the contrast in a diagnostically interesting part of the image, and the enhancement of the image.
When image processing is performed in the image encoding and recording unit, processed images are recorded and analysis techniques can no longer be applied to the "raw" images. Such analysis techniques are diagnostically important, because they enable determination of important parameters, for example the volume of the left ventricle in the case of cardiography. The application of analysis techniques to processed images has the serious drawback that the result is rendered dependent on the image processing algorithm used. A second drawback resides in the fact that image processing modifies the image, such as increased image sharpness and hence also increased noise, so that loss-free compression with an acceptable compression factor becomes impossible. Image compression is often necessary because of the large number of images involved in, for example cardiography, the finite storage capacity of the record carrier, and the limited speed of data transport to and from the record carrier.
Image processing in the image information retrieval unit is disadvantageous when a large number of images must be displayed within a short period of time, for example display of moving images in the form of a film. These moving images necessitate the use of a data stream with high compression so that, in combination with enhancement or increased contrast during the image processing, disturbing image artefacts are liable to occur.